Process for controlling the photocoagulation of biological tissue

Abstract

A process to control the extent of photocoagulation of the retina wherein light reflected from discrete portions (Ti) of the retina (75) in the eye is projected by a lens system (82) to individual photodiodes (DI) in an array (85) to generate electrical signals related to the light intensity reflected from a corresponding portion (Ti) on the retina (75) being treated. A change in the reflectance of any discrete portion (Ti) of an area on the retina relative to the reflectance of any discrete portion of the area on the retina actuates a control mechanism associated with laser (22). Upon a change to a threshold reflectance or a maximum rate of change in reflectance, a control apparatus (90) automatically adjusts parameters of treatment including power (22), focus (25) or sighting (102, 104).

Having described my invention, I claim: 
     
       1. A process for controlling the photocoagulation of biological tissue in which light is imaged on a zone which includes the area to be coagulated by a treatment light source and the region around it, comprising the steps of: measuring luminance in partial areas of the zone covering the area irradiated by the treatment light source and the region around it; determining values of luminance of the partial areas; comparing the determined values of the luminance of the partial areas and the quantities derived therefrom with predetermined values; and controlling irradiation by the treatment light source in response to a change in the luminance of a partial area of the zone relative to the luminance of the same or another partial area of the zone or of a partial area of the region around the zone. 
     
     
       2. A process according to claim 1 wherein partial areas are combined to form partial area groups and the combination of the partial areas to partial area groups is carried out on the basis of the measured luminances of the partial areas. 
     
     
       3. A process according to claim 2 wherein the combination of the partial areas to partial area groups take place in such a way that the surface contents of the partial area groups are predetermined and/or are of the same size, and/or that they are located along the lines of identical intensity within the intensity distribution of the intense light irradiation or the measuring radiation. 
     
     
       4. A process according to claim 1, wherein a pilot light source is imaged on the zone which includes the area to be coagulated by the treatment light source. 
     
     
       5. A process according to claim 4, wherein the treatment light source and the pilot light source are alternately used for measuring the luminances in the partial areas and the quantities derived therefrom in a predetermined manner. 
     
     
       6. A process according to claim 1, wherein the luminance is measured in transmission through the biological tissue. 
     
     
       7. A process according to claim 1, wherein the light of the treatment light source is used for measuring the luminance. 
     
     
       8. A process according to claim 1, wherein the area to be measured is imaged on an array of photodetectors and the individual photodetectors are interrogated for measuring the luminance. 
     
     
       9. A process of claim 1, wherein the area to be measured is imaged on a photodetector and the individual partial areas are successively scanned by a measured beam for measuring the luminance. 
     
     
       10. A process for controlling the photocoagulation of biological tissue comprising the steps of: imaging a pilot light source on a zone which includes an area to be coagulated by a treatment light source; dividing the zone into an array of individual partial areas; combining individual partial areas to form a plurality of partial area groups; and controlling photocoagulation by a treatment light source when one or more of the following derived quantities reaches a predetermined value: (a) the quotient of the momentarily measured luminance of a partial group in the array divided the luminance in the same or a different partial area group measured at the start of irradiation,   (b) the difference between the momentarily measured luminance in a partial area group and the luminance of another partial area group,   (c) the quotient of the momentarily measured luminance of a first partial area group divided by the momentarily measured luminance of another partial area group,   (d) the difference of the quotient of the momentarily measured luminance in a first group divided by the luminance in the same partial area group measured at the start of irradiation and the quotient of the momentarily measured luminance of a second group divided by the luminance of the second group measured at the start of irradiation,   (e) the time interval for a specified change in luminance in a partial area group,   (f) the difference between the time interval of a specified luminance change in two different subgroups,   (g) the quotient of the time interval required for a specified luminance change in a first partial group divided by the time interval for a specified luminance change in a second partial area group,   (h) the time gradient of the luminance in a partial area group,   (i) the difference between the gradient of the luminance in a first partial area group and a second partial area group,   (j) the quotient of the time gradient of luminance in a first partial area group divided by the time gradient of luminance in a second partial area group,   (k) the spatial gradient of the luminance of a partial area group   
     
     
       11. A process for controlling the photocoagulation of biological tissue comprising the steps of: focusing a pilot light source to illuminate an area around a target area; providing an array of diodes; directing light reflected from each of a plurality of discrete portions of the illuminated area to corresponding photodiodes in the array; delivering a treatment beam having a wave length different from the wave length of the pilot light source to a target area inside the illuminated area; and controlling the treatment beam in response to changes in reflected light to a diode in the array of diodes resulting from changes in the tissue in the target area. 
     
     
       12. The process of claim 11 wherein the step of controlling the beam comprises: moving the beam across the tissue. 
     
     
       13. The process of claim 11 wherein the step of controlling the beam comprises: controlling the intensity of the treatment beam. 
     
     
       14. The process of claim 11, the step of controlling the treatment beam in response to changes in reflected light comprising the steps of: combining individual photodiodes to form groups of photodiodes corresponding to groups of discrete portions of the illuminated area; and controlling the treatment beam in response to relative values of luminance of the partial area groups. 
     
     
       15. A process for controlling the photocoagulation of biological tissue comprising the steps of: dividing a zone to be treated by a light source into a array of partial areas of the zone covering the area to be irradiated by an intense light source and the region around it; initiating irradiation by an intense light source; comparing characteristics of biological tissue in each partial area in the array with biological tissue in each of the partial areas at the start of the irradiation; and controlling irradiation in response to a pre-determined degree of change in characteristics of tissue in a partial area relative to the characteristics of biological tissue in a partial area of the array at the start of the irradiation.